The present invention relates to a damper valve mounted in vehicles such as motor vehicles and assembled to an oil-hydraulic circuit at place between an oil-hydraulic pump and a hydraulic actuator, as well as to a hydraulic power steering device using the same.
Hydraulic power steering devices for hydraulically assisting steering force have been widely used as a steering device for use in vehicles. The hydraulic power steering device is adapted to output a steering assist force by supplying a hydraulic actuator, such as a hydraulic cylinder, oil-hydraulic motor and the like, with a hydraulic oil outputted from an oil-hydraulic pump. Interposed between the oil-hydraulic pump and the hydraulic actuator is an oil-pressure control valve for controlling oil supply to the hydraulic actuator according to a steering direction and a steering resistance.
The hydraulic power steering device of this type may encounter a so-called shimmy phenomenon, in which vehicle wheels suffer excessive vibrations during normal drive due to poor precisions of parts of a steering system and such vibrations are transmitted to a steering wheel via, for example, a piston rod (rack shaft) of the hydraulic cylinder. In the general practice in the art, an arrangement for suppressing the shimmy phenomenon is made such that, for example, a check valve is disposed in the oil-pressure control valve for sealing the hydraulic cylinder, thereby allowing the hydraulic cylinder to act as a damper against the aforesaid vibrations.
However, the hydraulic cylinder acting as the damper involves the following problem. In a particular case where a driver abruptly turns the steering wheel to avoid danger, the hydraulic oil flowing back from either of the oil chambers to the oil-pressure control valve is blocked by the check valve so that the steering assist force is decreased. As a result, the driver manipulating the steering wheel encounters an abnormal load increase.
In an approach to overcome this problem, a damper valve is interposed in each oil-hydraulic circuit individually interconnecting either one of the laterally arranged oil chambers of the hydraulic cylinder and the oil-pressure control valve.
The damper valve is configured as shown in FIG. 8, for example. A movable valve 102 is accommodated in a hollow casing 101 as allowed to move along an oil passage therethrough. A check valve 104 including a ball 103 is formed within the movable valve 102, which is urged upwardly by a spring 105, as seen in the figure, so that an upper surface of the movable valve is in intimate contact with a throttle shoulder 106 of the casing 101. The movable valve 102 is formed with a plurality of communication holes 108 permitting the hydraulic oil to flow from a hydraulic cylinder (not shown) to an oil-pressure control valve 107 while the movable valve 102 is moved away from the throttle shoulder 106 against the urging force of the spring 105.
According to the damper valve 100, when the vibrations of vehicle wheels causes lateral vibrations of a piston rod of the hydraulic cylinder so that a fractional amount of hydraulic oil, based on the amplitudes of such lateral vibrations, is to be returned from the hydraulic cylinder to the oil-pressure control valve 107, an internal oil passage of the check valve 104 is closed by the ball 103 while the movable valve 102 is moved slightly away from the throttle shoulder 106 against the urging force of the spring 105. This permits the hydraulic oil to be returned to the oil-pressure control valve 107 through a minor gap 109 between the upper surface of the check valve 104 and the throttle shoulder 106 and through the communication holes 108 (see FIG. 9). In this process, the hydraulic oil is throttled down by the minor gap 109, thus producing a damper effect for suppressing the vibration transmission from the vehicle wheels to the steering wheel via the piston rod of the hydraulic cylinder.
In a case where the driver makes an abrupt steering, the hydraulic oil returned from either of the oil chambers of the hydraulic cylinder to the oil-pressure control valve 107 is increased in pressure to above a predetermined level so that the movable valve 102 is moved a great distance away from the throttle shoulder 106 against the urging force of the spring 105. This permits the hydraulic oil to be returned to the oil-pressure control valve 107 (see FIG. 10) via a major gap 110 between the upper surface of the check valve 104 and the throttle shoulder 106, and the communication holes 108. Hence, the occurrence of trouble, such as abnormal load increase of the steering wheel, may be prevented.
In the conventional hydraulic power steering device described above, the hydraulic oil is returned from the hydraulic cylinder to the oil-pressure control valve 107 via the minor gap 109 as follows. The hydraulic oil flowing down through a pipe 111 is deflected in lateral directions to be guided into the minor gap 109. Furthermore, the hydraulic oil flow is sharply deflected downward to be guided from the minor gap 109 into the communication holes 108. Accordingly, the flow resistance in the passage is increased to hinder a smooth flow of the hydraulic oil. Particularly when the vehicle wheels vibrate at abnormally high frequencies thereby causing oscillatory hydraulic pressures (fine, rapid pressure variations) in the hydraulic cylinder, the damper valve is decreased in response to the oscillatory hydraulic pressures to become incapable of effectively presenting the damper effect.
It is an object of the invention to provide a damper valve capable of effectively presenting the damper effect despite the oscillatory hydraulic pressures in the hydraulic actuator, and a hydraulic power steering device using the same.
The invention is directed to a damper valve disposed on an oil-hydraulic circuit extended between an oil-hydraulic pump and a hydraulic actuator operated by a hydraulic oil supplied by the oil-hydraulic pump, the damper valve comprising: a hollow casing having a first port connected to the oil-hydraulic circuit at place on an oil-hydraulic-pump side, and a second port connected to the oil-hydraulic circuit at place on a hydraulic-actuator side; a cylindrical movable valve disposed in the casing as allowed to move along an oil passage therethrough; a valve sleeve disposed in the casing and having a valve seat allowing the movable valve to be seated on one end surface thereof; a spring for urging the movable valve thereby bringing one end surface of the movable valve into intimate contact with the valve seat of the valve sleeve; a check valve disposed in the valve sleeve and operative to permit the hydraulic oil delivered by the oil-hydraulic pump to flow from the first port through the movable valve and the valve sleeve to the second port but to restrict the reversed flow of the hydraulic oil; and a communication path formed in the valve sleeve and opening into the valve seat for the movable valve at one end thereof thereby allowing for a smooth flow of the hydraulic oil from the second port into the movable valve moved away from the valve seat.
According to the damper valve of this configuration, the hydraulic oil through the oil-hydraulic circuit from the oil-hydraulic-pump side toward the hydraulic actuator is allowed by the check valve to flow from the first port through the movable valve and the valve sleeve to the second port so as to be supplied to the hydraulic actuator.
On the other hand, the hydraulic oil through the oil-hydraulic circuit from the hydraulic actuator toward the oil-hydraulic-pump side is prohibited by the check valve from flowing through the valve sleeve. Instead, the hydraulic oil is guided through the communication path to the valve seat of the valve sleeve so as to push the movable valve away from the valve seat. As a result, the hydraulic oil is returned through the oil-hydraulic circuit from the hydraulic-actuator side to the oil-hydraulic-pump side via the second port, communication path, the gap between the one end surface of the movable valve and the valve seat, and the first port. In this process, the communication path allows for a smooth flow of the hydraulic oil from the second port into the movable valve, thereby ensuring a preferable response to the oscillatory hydraulic pressures in the hydraulic actuator. Thus is accomplished a positive and effective reduction of the influences of disturbances attributable to low precisions of the vehicle components and driving environment, the disturbances including, for example, shimmy phenomenon, kickback phenomenon and the like.
The check valve may be of a unit assembled from a case fixed in the valve sleeve, a movable valve body accommodated in the case, and a valve seat member mounted in the case for allowing the movable valve body to be seated thereon. In this case, the check valve may be readily assembled in the valve sleeve.
The check valve may include a ball for closing an interior of the valve sleeve, and a lock plate serving to retain the ball within the valve sleeve and having a through hole allowing the hydraulic oil to flow therethrough. In this case, the check valve consists of a smaller number of components, contributing to a more simplified construction of the damper valve.
The invention is directed to a hydraulic power steering device comprising: an oil-hydraulic pump; a hydraulic actuator operated by a hydraulic oil supplied by the oil-hydraulic pump thereby outputting a steering assist force; an oil-pressure control valve disposed on an oil-hydraulic circuit at place between the hydraulic actuator and the oil-hydraulic pump and operative to control the supply/discharge of the hydraulic oil to/from the hydraulic actuator according to a steering operation; and the damper valve claimed in any one of claims 1 to 3 and disposed on the oil-hydraulic circuit at place between an output port of the oil-pressure control valve and the hydraulic actuator.
According to the hydraulic power steering device of this configuration, the hydraulic oil from the oil-pressure control valve toward the hydraulic actuator is allowed by the check valve to flow from the first port through the movable valve and the valve sleeve to the second port so as to be supplied to the hydraulic actuator.
On the other hand, the hydraulic oil from the hydraulic actuator toward the oil-pressure control valve is prohibited by the check valve from flowing through the valve sleeve. Instead, the hydraulic oil is guided through the communication path to the valve seat of the valve sleeve, thus pushing the movable valve away from the valve seat. As a result, the hydraulic oil is returned from the hydraulic actuator to the oil-pressure control valve via the second port, communication path, the gap between the one end surface of the movable valve and the valve seat, and the first port. In this process, the communication path allows for a smooth flow of the hydraulic oil from the second port into the movable valve. Therefore, even if the vehicle wheels vibrate at abnormally high frequencies to cause the oscillatory hydraulic pressures in the hydraulic actuator, a preferable response to the oscillatory hydraulic pressures is ensured. This provides for a positive and effective reduction of the influences of disturbances attributable to the low precisions of vehicle components and driving environment, the disturbances including, for example, shimmy phenomenon, kickback phenomenon and the like.